Seminars

Coming seminars

Past seminars

June, 18 2024. 10:00 Prof. Jérémy Bleyer, Research scientist at Laboratoire Navier, team Matériaux et Structures Architecturés.

  • Topic: Automating non-smooth convex optimization for structural engineering applications.
  • Place: Room A103 of INRIA Grenoble Rhone-Alpes, Montbonnot.
  • Abstract: Numerous problems in non-linear mechanics can be effectively addressed through a variational framework, often leading to convex yet non-smooth optimization problems. Leveraging the advancements in dedicated optimization solvers, we can now tackle large-scale problems, opening avenues for innovative applications. In this work, we discuss the automation of formulating PDE-based non-smooth optimization problems, leveraging the conic representation of convex functions and the automation capabilities of the FEniCSx finite-element software package [1]. We will present a panorama of mechanics problems amenable to this approach, spanning elastoplasticity and limit analysis of concrete and steel structures, nonlinear membranes, and viscoplastic fluids [2,3]. Finally, we also present an extension of these methodologies to shape optimization of civil engineering structures [4].
  • References:
  1. Bleyer, Jeremy. “Automating the formulation and resolution of convex variational problems: applications from image processing to computational mechanics.” ACM Transactions on Mathematical Software (TOMS) 46.3 (2020): 1-33. https://doi.org/10.1145/3393881
  2. Bleyer, Jeremy. “Applications of conic programming in non-smooth mechanics.” Journal of Optimization Theory and Applications (2022): 1-33. https://doi.org/10.1007/s10957-022-02105-z
  3. Bleyer, Jeremy. “Advances in the simulation of viscoplastic fluid flows using interior-point methods.” Computer Methods in Applied Mechanics and Engineering 330 (2018): 368-394. https://doi.org/10.1016/j.cma.2017.11.006
  4. Mourad, Leyla, et al. “Topology optimization of load-bearing capacity.” Structural and Multidisciplinary Optimization 64.3 (2021): 1367-1383. https://doi.org/10.1007/s00158-021-02923-1
(Internal Seminar)
April, 9 2024. 10:00 Dr. Simon Le Berre, Postdoctoral fellow. TRIPOP team
  • Topic: Model order reduction for quasi-static contact mechanics
  • Abstract: We are interested in model order reduction of contact mechanics problems treated by Lagrange multipliers, which remains a scientific challenge, in particular due to the non negativity constraint on the multipliers. This work relies on Hyper-Reduced order modelling, which is an efficient strategy to deal with nonlinearities. We consider here its extension to contact mechanics. A Hybrid Hyper-Reduced (HHR) model is built, using a reduced integration domain (RID), a POD (Proper Orthogonal Decomposition) primal reduced basis (RB), and a dual reduced basis obtained by restriction of the dual finite element (FE) basis to the RID. The HHR model inherits its saddle-point formulation from the FE problem. We propose in this work a theoretical and numerical analysis of the HHR model. First, error bounds of the HHR model are theoretically demonstrated. Thanks to the dual reduced basis construction by restriction to the reduced domain, Céa type error estimators are obtained instead of classical Brezzi estimators classically derived for mixed problems. Hence, the primal error is independent from the dual approximation, while the dual error only depends on the primal error and on the inf-sup/LBB constant of the HHR model. A posteriori error estimators are also derived, allowing for the development of a new efficient error indicator. These error estimations pave the way to automatic numerical strategies improving the dual precision of the HHR method.
    We propose two primal RB enrichment strategies that ensure the solvability (LBB/inf-sup condition) of the HHR problem while significantly improving the precision of the dual solutions. These enrichment strategies are based on the minimization of the condition number of the reduced contact rigidity matrix. In order to limit the  enrichment of the primal RB while still reducing the dual error, clustering methods on the parametric space are introduced. They consist in dealing with the nonlinear solution manifold in a piece-wise low-rank linear manner by building local reduced order models. We then look at the generalization of the HHR model to non-matching contact meshes. By construction, the HHR model is a Petrov-Galerkin projection of the FE saddle-point problem. This projection leads to a generalized saddle-point problem (non block-symmetric) when node-to-surface contact conditions are considered. The generalized HHR problem, under associated solvability conditions, is then solved using a dedicated solver. Moreover, the HHR method inherits the Hyper-Reduction’s ability to efficiently treat nonlinear mechanics problems. Hence, unilateral contact problems between deformable nonlinear materials can be reduced with the HHR method, which goes beyond the current state-of-the-art. Accurate results obtained on a industrial example of interest confirms the high potential of the HHR method.
  • Place: The seminal will held in Room A103 of INRIA Grenoble center.
 
(Internal Seminar)
Mar, 21 2024. 10:00 Louis Guillet. PhD student. TRIPOP team
  • Topic: Numerical Simulation of Gravity Flows : Non-smooth MPM for Simulations of Geomaterials
  • Abstract: Gravity flows are responsible for many casualties every year in the alpine region, and being able to simulate them precisely is a major issue for risk assessment. This work focuses on an implicit, non-smooth approach to simulate geomaterials within the scope of non-associative elasto-plasticity. This approach, derived from the Implicit Standard Material, is compatible with many space discretization techniques, particularly the Material Point Method and the Finite Element Method. We evaluate the performance of the solver, namely its quadratic convergence, through MPM footing simulation.
  • Keywords: Material Point Method, Non-Smooth Dynamics, Non-Associative Plasticity, Complementarity Based Solvers
  • Place: The seminar will held in Room F107 of INRIA Grenoble center.

Mar, 12 2024.  09:00 Prof. Antonio Joaquin Garcia Suarez. EPFL, Lausanne, Switzerland
  • Topic: Phase-space iterative solvers
  • Abstract:
    This talk introduces an iterative method to solve problems in small-strain non-linear elasticity, inspired by recent work in data-driven computational mechanics, which reformulated the classic boundary value problem of continuum mechanics using the concept of “phase space”. The latter is an abstract metric space, whose coordinates are indexed by strains and stress components, where each possible state of the discretized body corresponds to a point. Since the phase space is associated to the discretized body, it is finite dimensional. Two subsets are then defined: an affine space termed “physically-admissible set” made up by those points that satisfy equilibrium and a “materially-admissible set” containing points that satisfy the constitutive law. Solving the boundary-value problem amounts to finding the intersection between these two subdomains. The method consists on projecting points alternatively from one set to the other, until convergence, in similar in spirit to the “method of alternative projections” and to the “method of projections onto convex sets”.
  • bio: Joaquin earned his “Ingeniero Industrial” diploma from University of Seville in 2013 and M.Sc. and PhD in Aeronautics (minor in Applied Mathematics) from the California Institute of Technology in 2016 and 2020, respectively. After a 2.5-year postdoc at Prof. Molinari’s group at EPFL (LSMS), in January 2023 he became SNSF Ambizione fellow at the same institution. His current research hinges on three intertwined themes: data-driven mechanics, vibrations and interface mechanics.
  • The seminar will held in Room A103 of INRIA Grenoble center.
Mar, 12 2024.  10:30 Prof. Konstantinos Karapiperis, ETH, Zurich, Switzerland
  • Topic: Recent advances in data-driven multiscale computational mechanics
  • Abstract:
    This presentation introduces recent developments in the field of data-driven multiscale computational mechanics. In the first part, I discuss how we can leverage the data-driven computing paradigm where the material dataset is constructed from lower-scale calculations. Emphasis is placed on resolving history dependence, as well as tackling data scarcity through an adaptive sampling strategy. Examples to be drawn include the failure of granular solids by shear banding or by grain fracture under high confining pressures. In the second part, I will focus on the multiscale analysis of materials from a different perspective, in which the mechanical behavior at a lower scale is approximated using machine learning techniques. In this case, I showcase examples from the simulation of polymer-based architected materials at large deformations.
  • bio: Konstantinos (Kostas) Karapiperis is currently a Postdoctoral Scientist and Lecturer at ETH Zurich, and an incoming Assistant Professor at EPFL. He earned his Diploma in Civil Engineering from NTUA, Greece, his M.Sc. in Geomechanics from University of California, Davis, and his PhD in Applied Mechanics (minor in Applied Mathematics) from the California Institute of Technology. His research focuses on the mechanics of failure in microstructured solids (e.g. instabilities in granular materials and geomaterials, inelasticity and fracture of architected and structural materials, failure of frictional intefaces and fibrous materials) through the development of multiscale and data-driven techniques.
  • The seminar will held in Room A103 of INRIA Grenoble center.
Jan, 16 2024.  14:00 Prof. Michael Muehlebach, Learning and Dynamical Systems group at the Max Planck Institute for Intelligent Systems, Germany.
  • Topic: Accelerated First-Order Optimization under Nonlinear Constraints
  • Abstract: My talk will explore analogies between first-order algorithms for constrained  optimization and non-smooth dynamical systems for designing a new class of accelerated first-order algorithms for constrained optimization. Unlike Frank-Wolfe or projected gradients, these algorithms avoid optimization over the entire feasible set at each iteration. I will highlight various convergence results in a convex and nonconvex setting and derive rates for the convex setting. An important property of these algorithms is that constraints are  expressed in terms of velocities instead of positions, which naturally leads to sparse, local and convex approximations of the feasible set (even if the feasible set is nonconvex). Thus, the complexity tends to grow mildly in the number of decision variables and in the number of constraints, which makes the algorithms suitable for machine learning  applications. I will further discuss numerical results, where I applied the algorithms to a compressed sensing and a sparse regression problem, showing that nonconvex lp constraints (p<1) can be treated efficiently, while state-of-the-art performance is recovered for p=1.
  • References:
  • The seminar will held in Room F107 of INRIA Grenoble center.
(Internal Seminar)
Dec, 7 2023. Dec, 14 2023.  10:00 Aya Younes. PhD student. TRIPOP team
  • Topic: Trajectory Tracking in Nonsmooth Mechanical System with Set-valued Friction
  • Abstract:This work tackles the trajectory tracking problem in nonsmooth mechanical systems with set-valued friction. The well-posedness and stability of the frictional oscillator with Coulomb’s friction are analyzed in the complementarity system framework. Then, the stability of the closed-loop system is introduced under a passivity-based control strategy. Parametric robustness analysis is examined, focusing on the Stribeck model of sliding friction.
  • The seminar will held in Room F107 of INRIA Grenoble center.
(Internal Seminar)
Nov, 23 2023. 14:30 Quang Hung Pham. PhD student. TRIPOP team
  • Topic: Control and analysis of nonlinear and multivalued networks.
  • Abstract:Derived from a diverse range of applications in various fields, including mechanics, physics, robotics, traffic flow, economics, etc., Linear Complementarity Systems (LCS) have been extensively investigated as a crucial class of dynamical systems. The well-posedness (i.e., the existence and uniqueness of a solution) of LCS is provided in [1,2]. In reality, the presence of time-varying perturbations leads to the emergence of a class of time-varying systems, extending beyond LCS, referred to as the Time-varying Linear Cone Complementarity System (TVLCCS). The novel challenges we face revolve around establishing the well-posedness of this class, and that is the core focus of this talk. Consider a TVLCCS. For the case D(t) is positive semidefinite, we will present a set of sufficient conditions, based on the transformation proposed in [3] and a slightly extended version of [1], ensuring the existence and uniqueness of an absolutely continuous solution for TVLCCS. This result serves as an extension of [1]. The case where D(t) is positive definite can be solved using [4]. We also consider a special case, D(t) is a zero matrix as it finds application in various fields and the results are provided in there that extend [2] and point out the well-posedness of a right-continuous bounded variation solution.[1] M.K. Camlibel, L. Iannelli, and A. Tanwani. Convergence of proximal solutions for evolution inclusions with time-dependent maximal monotone operators. Mathematical Programming, Series A, July 2021.
    [2] B. Brogliato and L. Thibault. Existence and uniqueness of solutions for non-autonomous complementarity dynamical systems. Journal of Convex Analysis, 17(3-4):961–990, 2010.
    [3] A. Tanwani, B. Brogliato, and C. Prieur. Well-posedness and output regulation for implicit time-varying evolution variational inequalities. SIAM Journal on Control and Optimization, 56(2):751–781, 2018.
    [4] H. Cartan. Cours de Calcul Différentiel. Hermann, Paris, France, 1977.
  • The seminar will held in Room F107 of INRIA Grenoble center.
Oct, 26 2023. 10:00 F. Castaños Luna. Departamento de Control Automático, CINVESTAV-IPN, Mexico.
  • Topic: Equivalence of Linear Complementarity Problems: Theory and Application to Nonsmooth Bifurcations.
  • Abstract:
    Linear complementarity problems provide a powerful framework to model nonsmooth phenomena in dynamical control systems. Mimicking the general strategy that led to the foundation of bifurcation theory in smooth maps, we introduce a novel notion of equivalence between linear complementarity problems that sets the basis for a theory of bifurcations in a large class of nonsmooth maps, including steady-state bifurcations in linear complementarity systems. Our definition leads to constructive algebraic conditions for identifying and classifying the nonsmooth singularities associated with nonsmooth bifurcations. We thoroughly illustrate our theory on an extended applied example and on the identification and classification of all possible equivalence classes in two-dimensional linear complementarity problems.
  • The seminar will held in Room F107 of INRIA Grenoble center.
Jun, 29 2023. 10:00 A. Pinto da Costa. Departamento de Engenharia Civil, Instituto Superior Técnico et CERIS. Universidade de Lisboa.
  • Topic: Applications en Mécanique du “cone-constrained eigenvalue problem” : flambement et frottement
  • Abstract:
    Nous traitons certains des aspects mécaniques et algébriques du problème de recherche des instabilités directionnelles dans le contexte du contact unilatéral sans ou avec frottement. D’un point de vue plus général, il s’agit de résoudre des problèmes d’instabilité de systèmes non réguliers ; c’est à dire, de vérifier si les conditions existent pour l’apparition des solutions dynamiques non oscillatoires exponentiellement croissantes avec des conditions initiales arbitrairement proches d’un état d’équilibre d’un système non régulier, sans recours à aucune régularisation. Ingrédients comme la “raideur élastique”, la “raideur géométrique”, le “frottement”, la “courbure de l’obstacle” et la “distribution spatiale des réactions de l’obstacle”, convenablement combinés, jouent un rôle important.

     

    Le problème algébrique qui est derrière l’étude des instabilités directionnelles est un problème aux valeurs propres de type spécial : un problème aux valeurs propres dont les inconnues appartiennent à des cônes et satisfont des conditions de complémentarité. Le problème de complémentarité aux valeurs propres en cônes continue à attirer une certaine attention dans les communautés Mathématique et Mécanique ; sont caractère combinatoire pose des défis évidents. Une collaboration entre mécaniciens et mathématiciens sur ce problème apportera certainement des avantages mutuelles car il reste encore beaucoup à explorer d’une part et de l’autre.

  • The seminar will held in Room F107 of INRIA Grenoble center and zoom https://univ-grenoble-alpes-fr.zoom.us/j/6124083093 .
Feb. 09 2023. 10:30 Louis Guillet PhD Student TRIPOP
  • Topic: Depth-averaged material point method to simulate the release of snow avalanches over complex 3D terrain.
  • Abstract:
    Snow slab avalanches release due to crack propagation within a weak snow layer buried below a cohesive snow slab. The first model described this process assuming an interfacial and quasi-brittle shear failure for the weak layer. This model fails to explain observations of propagation on low angle terrain and remote avalanche triggering. To address this shortcoming, the anticrack concept, developed for porous rocks was adapted in 2008 to weak snow layers. Later models showed that mixed mode shear-compression failure and subsequent volumetric collapse (anticrack) of the weak layer were necessary ingredients to accurately model propagation mechanisms, thus reconciling apparently conflicting theories. More recently, large scale simulations based on the Material Point Method (MPM) and field observations revealed a transition from slow anticrack to fast supershear crack propagation. This transition, which occurs after a few meters suggests that a pure shear model should be sufficient to estimate the release sizes of large avalanche release zones.

     

    Motivated by this new understanding, we developed a depth-averaged MPM for the simulation of snow slab avalanches release. Here, the weak layer is treated as an external shear force acting at the base of the slab and is modeled as an elastic quasi-brittle material with residual friction. We first validate the model based on simulations of the so-called Propagation Saw Test (PST) and comparing numerical results to analytical solutions and 3D simulations. Second, we perform large scale simulations and analyse the shape and size of avalanche release zones. Finally we apply the model to a complex real topography. Due to the low computational cost compared to 3D MPM, we expect our work to have important operational applications for the evaluation of avalanche release sizes required as input in hazard mapping model chains. Finally, the model can be easily adapted to simulate both the initiation and dynamics of shallow landslides.

  • The seminar will held in Room F107 of INRIA Grenoble center and zoom https://univ-grenoble-alpes-fr.zoom.us/j/6124083093 .
Dec. 06, 2022. 10:00 Mazen Alamir  Univ. Grenoble Alpes, CNRS, Grenoble INP, GIPSA-lab. 
  • Topic: Learning against uncertainty in control engineering
  • Abstract: In this talk, some data-based control design options that can be used to accommodate for the presence of uncertainties in continuous-state engineering systems are recalled and discussed. Focus is made on reinforcement learning, stochastic model predictive control and certification via randomized optimization. Some thoughts are also shared regarding the positioning of the control community in a data and AI-dominated period for which some suggestions and risks are highlighted.
  • References: [1] Mazen Alamir. Learning against uncertainty in control engineering, Annual Reviews in Control, Volume 53, 2022, Pages 19-29,
  • The seminar will held in Room F107 of INRIA Grenoble center
Oct. 20, 2022. 10:00 Hoang Minh Nguyen PhD Student. Tripop
  • Topic:  High-accuracy computation of rolling friction contact problems
  • Abstract: Our aim is to perform numerical solutions of an optimization model derived from the problem of unilateral contact between solid bodies with rolling friction. The model is an optimization problem with a strictly convex quadratic objective function and a second-order cone of constraints that is not self-dual. The solver is an implementation of a primal-dual interior-point algorithm with the predictor-corrector scheme of Mehrotra extended to second-order cone problem. We focused on the analysis of the limits of numerical computation and propose some treatments to achieve optimal solutions with ten significant digits precision.
  • The seminar will held in Room F107 of INRIA Grenoble center
  • References:
    [1] Vincent Acary, Paul Armand, Minh Hoang. High-accuracy computation of rolling friction contact problems. {date}. ⟨hal-03741048⟩
Oct. 11, 2022. 10:00 Ramon Verdes Kairuz
PhD Student. CITEDI-IPN Mexico 
  • Topic:  Prescribed-time stabilization of controllable planar systems using switched state feedback
  • The seminar will held in Room F107 of INRIA Grenoble center
Sep. 08, 2022. 10:00 Ioannis Stefanou  Professor Ecole Centrale Nantes, France. 
  • Topic : Preventing earthquake instabilities
  • Abstract : Earthquakes nucleate when large amounts of elastic energy are suddenly released due to abrupt sliding over seismic faults. Besides physical causes, this energy release can be also triggered by injecting large amounts of fluids in the earth’s crust. Indeed, recent experience shows that injections can reactivate existing seismogenic faults and induce/trigger earthquakes of significant magnitude [see 1,2].However, one can see the problem of fluid injections from another perspective [3]. The dependence of fault friction on fluid pressure can be used as an input for stabilization. New results based on the mathematical theory of control show that (a) it is indeed possible to stabilize and restrict chaos in this kind of non-linear, unstable frictional systems and (b) assure slow frictional dissipation toward desirable global asymptotic equilibria of lower potential energy. Our theoretical results are validated through a series of numerical analyses and experimental tests using full and reduced order models of seismic faults [4-9].
  • Short Bio: Ioannis Stefanou is Professor at Ecole Centrale de Nantes (ECN), France. He studied civil engineering, mechanics and applied mathematics at the National Technical University of Athens. He then did his PhD thesis at the Laboratory of Geomaterials of the same institution. His main research topics are the mechanics of (geo-)materials, structural dynamics, geomechanics, fault reactivation and earthquake control, bifurcation theory, homogenization and higher order continua. He is the PI of the ERC-StG project “Controlling earthQuakes – CoQuake” (www.coquake.eu) and of the Connect Talent project “Controlling Extreme EVents – CEEV” (www.blastructures.eu) awarded by the Pays de la Loire.
  • References:[1] Zastrow, M. (2019). South Korea accepts geothermal plant probably caused destructive quake, 2019, https://doi.org/10.1038/d41586-019-00959-4
    [2] https://www.lemonde.fr/planete/article/2020/12/07/apres-une-serie-de-seismes-arret-definitif-du-projet-de-centrale-geothermique-a-strasbourg_6062543_3244.html
    [3] Stefanou, I. (2020). Conference TEDx Rennes « Maîtriser les séismes… et pourquoi pas ?, https://www.tedxrennes.com/project/ioannis-stefanou/#
    [4] Stefanou, I. (2019). Controlling Anthropogenic and Natural Seismicity: Insights From Active Stabilization of the Spring‐Slider Model. Journal of Geophysical Research: Solid Earth, 124(8), 8786–8802. https://doi.org/10.1029/2019JB017847
    [5] Stefanou, I., Tzortzopoulos, G. (2022). Preventing instabilities and inducing controlled, slow-slip in frictionally unstable systems. Journal of Geophysical Research: Solid Earth. https://doi.org/10.1029/2021JB023410
    [6] Tzortzopoulos G., Braun P., Stefanou I. (2021), Absorbent Porous Paper Reveals How Earthquakes Could be Mitigated, Geophysical Research Letters 48. https://doi.org/10.1029/2020GL090792.
    [7] Gutiérrez-Oribio D., Tzortzopoulos G., Stefanou I., Plestan F. (2021). Earthquake Control: An Emerging Application for Robust Control. Theory and Experimental Tests. http://arxiv.org/abs/2203.00296
    [8] Papachristos, E., Stefanou, I. (2021), Controlling earthquake-like instabilities using artificial intelligence. Pre-print: http://arxiv.org/abs/2104.13180.
    [9] Gutiérrez-Oribio D., Stefanou I., Plestan F. (2022). Passivity-based Control of a Frictional Underactuated Mechanical System: Application to Earthquake Prevention, to be submitted.
  • The seminar will held on zoom.
Apr. 21, 2022. 11:00 Maksym Shpakovych PhD candidate XLIM Limoges  
  • topic : Machine learning algorithm applied to the phase control of an array of laser beams
  • Abstract : GRENOBLE_2022_abstract
  • The seminar will held in Room F107 of INRIA Grenoble center

 

Apr. 15, 2021. 11:00 Vincent Richefeu Professor 3S-R lab UGA  
  • topic : Modélisations numériques discrètes : fondements et extensions
  • Abstract : Il existe de nos jours une multitude d’approches basées sur des éléments distincts. La méthode en éléments discrets (DEM) classique, dite “de Cundall”, est la plus utilisée ; souvent pour modéliser des milieux granulaires. Selon la problématique traitée, d’autres approches peuvent être plus appropriées. Parmi elles, la Dynamique des Contacts, la méthode Quasi-Statique ou “pilotée par des événements” (Event Driven) sont des alternatives qui présentent des intérêts différents. Dans cette présentation, après un rapide aperçu de l’approche DEM classique, je présenterai divers enrichissements possibles selon divers cheminements. (1) L’utilisation de lois d’interaction perfectionnées, notamment pour la prise en compte de la présence de petites quantités de liquide entre les particules. (2) La prise en considération explicite de formes complexes des particules, ces formes pouvants être concaves. (3) Un couplage “bord-à-bord” de la DEM avec une méthode de mécanique des fluides numérique (CFD) ; ici, ce sera la Méthode de Lattice Boltzmann (LBM) pour tous les degrés de saturation. Et finalement (4) un couplage double-échelles où le modèle constitutif d’une approche continue est remplacé par une Loi Homogénéisée Numérique à base de DEM ; il s’agira ici de FEMxDEM et de MPMxDEM. L’exposé sera illustré d’exemples d’utilisation des enrichissements présentés, mais il se voudra plutôt axé sur leurs caractères numériques.
  • The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
Jan 21, 2021. 11:00 Dr Mohammad Rasool Mojallizadeh Postdoctoral research engineer in TriPOP team at INRIA Rhône-Alpes; LJK, UGA
  • topic : Time-discretizations of differentiators: design of implicit algorithms, and comparative analysis
  • Abstract : A complete review of the known differentiators and their time-discretizations have been addressed in this study. To solve the drawbacks of the explicit (forward Euler) discretization, which is commonly utilized in sliding-mode-based differentiators, implicit time discretization methods are proposed to handle the set-valued functions. The proposed schemes are supported by some analytical results to show their crucial properties, e.g., finite-time convergence, exactness, invariant sliding-surface, chattering elimination, insensitivity to the gains during the sliding-phase, and the well-posedness. The causal implementation of the proposed implicit schemes has been addressed clearly and supported by flowcharts. Semi-implicit schemes are also presented to provide a compromise between the performance and the ease of implementation. Finally, an exhaustive comparison is made using numerical simulations and practical experiments among 25 different state-of-the-art differentiators to evaluate the behaviors of the differentiators under different conditions. General conclusions are that implicit discretizations supersede explicit and semi-implicit ones.
  • The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
  • Slides : DIGIT_SLID_Final.pdf
 

Dec 10, 2020. 11:00 Dr Nicholas Collins-Craft. TRIPOP team. INRIA
  • topic : Predicting strain localisation in crushable granular media using the Cosserat continuum
  • abstract: coming soonA consistent feature of the most destructive geological phenomena that humanity must live with, earthquakes and landslides, is the formation of thin bands featuring intense shearing that to a large extent control the global behaviour. While significant progress has been made in modelling these bands using the Cosserat continuum, existing models rely on a static mean grain size for their internal length scale. However, examination of shear bands in both the field and the laboratory reveals an extremely wide range of grain sizes due to the process of grain cataclasis, meaning that the modelling assumption of constant mean grain size is physically unjustifiable. In order to repair this defect, we first conducted some experiments to examine the effect of grain size polydispersity on shear band width. Then, using the results of these experiments and by coupling the Cosserat continuum with Breakage Mechanics, we obtained a model capable of predicting shear band formation in crushable granular media with an evolving grain size distribution. Finally, we examined the performance of this model in loading conditions analogous to the fast undrained shearing seen in earthquakes, and were able to explain the formation of “double shear bands” that are occasionally observed in the field.
  • info : The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
Dec 03, 2020. 11:00 Charlélie Bertrand. TRIPOP team. INRIA
  • topic : Dynamics of hauling rope : from curvilinear domains to its numerical computation
  • abstract : The presentation will be present a unified framework to compute the equilibrium of cable systems via Finite Element Methods. Starting from the equations of the curvilinear domains, it will be presented how the formulation of the problem has been adapted in order to account for non–compressibility of the media and the presence of obstacles with a particular interest for the practical case of a hauling rope (or telepheric installation).
  • info : The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
Nov 26, 2020. 11:00.  Dr Alexandre Rocca TRIPOP team. INRIA
  • topic : Nonsmooth methods for switching DAEs
  • abstract: In this work, we study how to apply methods from nonsmooth dynamics to ease the modelling and the simulation of multi–mode (also called hybrid) Differential Algebraic Equations (DAEs). This work is motivated by applications to the modelling energetic systems such as power–plants or energetic grids. In particular, we study how the nonsmooth dynamic formulations can be used to efficiently simulate multi–mode thermodynamic models such as such as the seven–equations models used by EDF to model phase changes. Such models are usually complex to simulate with the classical multi–mode approach. On a few examples, we show that our numerical methods can be used to simulate nonsmooth phase change models built from original EDF multimode models. We also show the current limitations of our approach and propose some guidelines to avoid them.
  • The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq

 

Nov 12, 2020. Dr Abhishek Chatterjee TRIPOP team. INRIA
  • topic : Modeling and simulation of multi-point collisions in rigid body systems
  • Abstract :This work presents a modeling and simulation technique for multi-point indeterminate (underdetermined) contact and impact problems in rigid body dynamic systems. Impacts between rigid bodies are characterized by discontinuous changes in velocities of the system, and therefore are modeled in impulse-domain. In the proposed framework impacts are treated as discrete events during which the velocities of the system evolve in the impulse-domain. Constraints derived based on the rigid body assumption are used to resolve indeterminacy associated with multi-point analysis. Also, a global energetic coefficient of restitution is proposed and used in this work, which characterizes the net energy loss through the system during impact, and guarantees energy consistency. One drawback of impulse-domain rigid impact models is that certain states such as deformation, contact force and time are ignored. This lost information can be useful for certain types of applications, where the contact force-history of an impact is of importance. Hence, the second part of this work presents an augmented rigid-impact model, which considers a contact force model from the contact mechanics literature along with the rigid impact model to also simultaneously determine the force and deformation histories during an impact event.
  • info : The seminar hold on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
 
Jan 14, 2020. Pr Nicolas Moes. Ecole Centrale de Nantes, GeM, UMR CNRS 6183. Institut Universitaire de France
  • topic : Yet another way to solve LCP problems emanating from variational inequalities : the Inequality Level Set approach (ILS).
  • abstract:Variational inequalities when discretized in the usual way yield a linear complementarity problem (LCP). We discuss in the presentation a new approach in which the variational inequality is formulated in a different but equivalent way. The main unknown is the interface separating the active and inactive zones. By active we mean the domain over which the constraint is active. The equation governing the interface evolution is in general a variational equality (thus removing the need for a LCP solver).The approach is coined ILS for Inequality Level Set because a level set field is used to locate the interface. The ILS approach uses the mathematical tools of configurational mechanics since the interface is not material but immaterial in nature (configurational). Contact and bounded strain models are considered to demonstrate the capability of the ILS (see references).ReferencesGraveleau, M., Chevaugeon, N., & Moës, N. (2015). The inequality level-set approach to handle contact: membrane case. Advanced Modeling and Simulation in Engineering Sciences, 2(1), 16. https://doi.org/10.1186/s40323-015-0034-8Bonfils, N., Chevaugeon, N., & Moës, N. (2012). Treating volumetric inequality constraint in a continuum media with a coupled X-FEM/level-set strategy. Computer Methods in Applied Mechanics and Engineering, 205–208, 16–28 https://doi.org/10.1016/j.cma.2011.02.012
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 11:00
May 16, 2019. Dr Michael Brun, INSA-Lyon, Lyon, France
  • topic : Applications of subdomain coupling methods to structural dynamics and multiphysics
  • abstract: The increasing complexity of numerical models for engineering systems, taking into account ever finer mesh, accurate material models and multiphysics phenomena, occurring at very different space and time scales, boosted the development of partitioning approaches. In the field of structural dynamics, the main advantage of partitioning approaches is to gain in computational efficiency by using different time integrators with their own time step, depending on the non-overlapping subdomains composing the global mesh. First, subdomain coupling methods have been set up, following an energy-based argument, leading to the proposition of Hybrid Asynchronous Time Integrator (HATI), stable and second or first order accurate depending on the ratio between the time scales. A large variety of applications of the HATI is then presented in the fields of structural dynamics, soil-structure interaction (SSI) and fluid-structure interaction (FSI): reinforced concrete subjected to earthquake or blast loading, crane bridge under earthquake loading experiencing non smooth dynamics phenomena, wave propagation in unbounded soil domains by introducing Perfectly Matched Layers (PML), SSI problems by coupling seismology SEM (Spectral Element Method) code with a FEM code, FSI problems by coupling SPH (Smooth Particle Hydrodynamics) and FV (Finite Volumes) methods for the fluid with FEM code for the structure. The last application developed within LSMS laboratory, EPFL, concerns the simulation of an unbounded elastic block on a rigid flat plane, involving rate and state friction laws at the interface, compared to classical Coulomb’s law with constant friction coefficient.
  • Bio: Dr Michael BRUN is a teacher and researcher at INSA-Lyon, in civil engineering laboratory GEOMAS. His research interests focus on the computational science in dynamics, applied to civil engineering structures and multiphysics coupling problems such as soil-structure and fluid-structure interactions. He got his PhD at INSA-Lyon in 2002 and worked during three years as an engineer in a private company (EC2-Modélisation, Lyon) specialized in simulations and software development. Since 2005, he has joined INSA-Lyon where he holds the position of Associate Professor, teaching continuum mechanics, strength of materials and numerical methods in the civil engineering and urban planning Department of INSA-Lyon. He spent one year in LSMS laboratory, EPFL, as a visiting professor in 2018 to develop efficient coupling approaches for soil-structure interaction problems as well as algorithms for rate and state friction laws at the interface between sliding rock blocks.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 14:00
 
April 04, 2019. Rami Sayoud, INRIA, Schneider Electric
  • topic : Vibrations analysis of electrical switchboards
March 29, 2019. Hugo Parada, UTFSM, Chile and INRIA France
  • topic : Lur’e systems stability properties and numerical simulations
October 12, 2018. Mathias Legrand, McGill University, Canada.
  • topic : Nonsmooth modal analysis overview
  • abstract: Nonsmooth modal analysis aims at computing modeshapes and attendant frequencies of vibration of structural systems subject to unilateral contact constraints. Nonsmooth modes of vibration are defined as one-parameter continuous families of nonsmooth periodic orbits satisfying the local equation together with the linear and nonlinear boundary conditions. A one-dimensional rod system is considered for illustration purposes with various boundary conditions one of which being unilateral. Semi-discretization in space via traditional Finite Element formulations is known to induce difficulties in the formulation, notably in the form of an impact law which generates chattering. Instead, the analysis is performed using the wave finite element method which is a shock-capturing finite volume method. The spectrum of vibration shown in the form of backbone curves provides valuable insight on the dynamics. In contrast to the linear system whose modes of vibration are standing harmonic waves, the nonsmooth modes of vibrations are traveling waves stemming from the unilateral contact condition. It is also shown that the vibratory resonances of the periodically driven system with light structural damping are well predicted by nonsmooth modal analysis. Furthermore, the initially unstressed and prestressed configurations exhibit stiffening and softening behaviors, respectively, as expected. Possible extensions in multi- dimensional frameworks are suggested.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 14:00
October 11, 2018. Mathieu Rupin, Hap2U, France.
  • topic : A programmable haptic interface based on ultrasonic lubrication
  • abstract: Les interfaces tactiles – écran + capteur de position du doigt – se sont démocratisées, au point d’avoir investi tous les secteurs des interfaces homme-machine. Cependant, ces interfaces présentent un défaut majeur : on ne peut pas les utiliser sans regarder l’écran. Cela pose des problèmes de sécurité qui limitent encore leur déploiement (l’automobile en est le parfait exemple). hap2U a développé une technologie basée sur la mise en vibration, à des fréquences ultrasonores, de la surface de l’interface permettant de stimuler la pulpe du doigt de l’utilisateur et ainsi créer une sensation de texture (retour haptique). Le principe physique sur lequel repose cette technologie est la lévitation acoustique qui permet de modifier le coefficient de frottement du doigt. Afin de parvenir à proposer une expérience utilisateur de qualité, différents aspects technologiques jouent un rôle clé : minimisation de la latence du dispositif, adaptation d’impédance électromécanique, interfaces dédiées. Au cours de ce séminaire je vous proposerai un survol de notre activité couvrant les aspects physico-physiologiques et techniques ainsi que les enjeux économiques.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, G220, 14:00
October 04, 2018. Sami Karkar, Ecole Centrale Lyon
  • topic : Manlab : non linéarités et solutions périodiques, une approche numérique.
  • abstract: Manlab est, à la base, un outil numérique de continuation de solutions de systèmes d’équations algébriques quadratiques. Vers la fin des années 2000, au LMA (Marseille), cette méthode a été couplée à l’équilibrage harmonique, une méthode spectrale globale, qui permet de discrétiser la solution périodique d’un système dynamique par une somme de Fourier (tronquée). On montrera comment le couplage de ces deux méthodes, et par la suite l’utilisation de la collocation par polynômes orthogonaux, permet de résoudre une très grande variété de problèmes issus de la physique. On s’est intéressé en particulier à des modèles physique d’instruments de musique comportant des non-linéarités liées à un écoulement et à du contact non frottant, comme les instruments à anche simple (clarinette, saxophone). On s’est également intéressé à des problèmes de frottements (application au violon), non réguliers donc, mais par… régularisation.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 11:00
  • topic : Vers une méta-matière programmable.
  • abstract : Les métamatériaux sont des cristaux artificiels, c’est à dire des
    matériaux structurés, obtenus par la répétition d’une cellule
    élémentaire, sous forme de réseau, et faisant apparaître des propriétés
    exotiques (masse ou une densité négative par exemple), à des fréquences
    basses, c’est à dire des effets “sub-longueur d’onde”. On s’intéressera
    dans cet exposé plus particulièrement à des métamatériaux acoustiques
    “smart”, c’est à dire dont les propriétés sont ajustables, voire
    programmables, par l’intermédiaire de micro-capteurs et actionneurs
    intégrés. A partir de cette brique de base programmable, on
    s’intéressera alors au couplage entre une milieu classique de
    propagation acoustique, et une condition aux limites non standard, par
    exemple une équation différentielle, obtenue directement en
    “programmant” notre métamatériaux. On peut pour la suite penser à des
    problèmes d’optimisation de l’opérateur à programmer sur les frontières
    du domaine en fonction d’une “fonctionnalité” macro attendue… A terme,
    on pourra également programmer des effets non-linéaires, et donc
    potentiellement élargir encore un peu plus l’espace dans lequel
    effectuer ces optimisations.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, C207, 14:00
September 26, 2018. Félix Miranda. U. Cambridge
  • topic : Analysis of low-dimensional attractors in linear complementarity systems
  • abstract: Dissipativity theory is a powerful tool for the analysis of stability of equilibria in linear and nonlinear systems. In this work, we present an extension of the classical dissipativity framework that is useful for the analysis of low dimensional attractors in linear complementarity systems. Examples illustrate the proposed approach.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 10:00
September 20, 2018. Stéphane Grange and David Bertrand, INSA Lyon
  • topic : “Vulnérabilité physique des structures dans un contexte de risques naturels. Application aux chutes de blocs et aux séismes.”
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 10:00
July 19, 2018. Thoi Thi Tran, Université de Limoges
  • topic : Numerical optimization for contact problems.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 10:00
July 4, 2018. Anindya Chatterjee from IIKT  (http://home.iitk.ac.in/~anindya)
June 28, 2018. Kirill Vorotnikov, TRIPOP Team
  • Topic :Application of numerical dissipation for the solution of multiple impacts problem in dissipative granular chains
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, C207, 11:00
March 29, 2018. Nicolas Molina Vergara, Pontificia Universidad Católica de Chile, Santiago, Chile.
  • Topic: “Alternating Direction Method of Multipliers (ADMM) for Frictional Contact”
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, C208, 11:00

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